p27Kip1 is an inhibitor of many cyclin dependent kinases (cdk) and is believed to be essential for the strict control of the cell cycle, both in vivo and in vitro. Human tumor cells usually do not have mutations in the p27Kip1 gene (Ponce-Castaneda, M. V. et al. (1995) Cancer Res., 55, 1211-1214), but they often have very low levels of the p27Kip1 protein. The low levels of the protein correlate with low survival rates of breast cancer (Porter, P. L. et al, (1997) Nat. Med., 3, 222-225; Loda, M. et al. (1997) Nat. Med., 3, 231-234), lung cancer (Esposito, V. et al. (1997) Cancer Res., 57, 3381-3385), prostate cancer (Yang, R. M. et al. (1998) J. Urol., 159, 941-945), and stomach cancer patients (Yasui, W. et al. (1997) Jpn. J. Cancer Res., 88.625-629). Moreover, a recent study showed that p27Kip1 was haplo-insufficient for tumor suppression (Fero, M. L. et al. (1998) Nature, 396, 177-180). This means that the tendency to form a tumor is increased by inactivation of one of the alleles or by a decrease in the expression of the protein. One of the most important strategies in cancer treatment is to revive the expression of tumor suppresser proteins. Therefore, p27Kip1 may be a useful molecule for cancer treatment. Recent research indicates that p27Kip1 mRNA levels are increased when neuroblastoma cells are incubated with a thyroid hormone, when embryonic carcinoma cells are incubated with retinoic acid, or when stomach cancer cells are incubated with interferon-β (Perez-Juste, G. and Aranda, A., (1999) J. Biol. Chem., 274, 5026-5031; Kawasaki, H. et al. (1998) Nature, 393, 284-289; Kuniyasu, H. et al. (1997) Cell Growth Differ., 8, 47-52). These results indicate that stability and levels of the p27Kip1 protein are increased by the up-regulation of p27Kip1 transcription. Therefore, it is assumed that regulation of p27Kip1 transcription has a more general importance. However, very little is known about the mechanism that regulates p27Kip1 transcription. The present inventors previously cloned the promoter region of the human p27Kip1 gene and discovered that the region between position −774 and −435 (relative to the transcription initiation site) was vital for promoter activity (Minami, S. et al. (997) FEBS Lett., 411, 1-6; Unexamined Published Japanese Patent Application No. (JP-A) Hei 11-137251).
1,25-dihydroxyvitamin D3 is not only a major regulator of mineral homeostasis but is also a potent modulator of differentiation in several types of cells, including monoblastic cells and osteoblasts (Minghetti, P. P. and Norman, A. W., (1988) FASEB J., 2, 3043-3053). Recent studies have revealed that the cdk inhibitors, p21Cip1 and p27Kip1, function as molecular switches that facilitate the vitamin D3-induced differentiation of the U937 myeloid leukemic cell line. These genes are regulated both at the transcriptional level and the post-transcriptional level by vitamin D3 during the early stages of this differentiation process (Liu, M. et al. (1996) Genes Dev., 10, 142-153). Vitamin D3 transduces its signal to the nucleus directly, mainly through a regulatable DNA-binding transcription factor, the vitamin D receptor (VDR) (Evans, R. M., (1988) Science, 240, 889-895). Also, ligand-inducible effects on differentiation are initiated through the direct activation of target genes by VDR. In fact, vitamin D3 induces p27Kip1 transcription in a VDR-dependent manner through a functional vitamin D response element (VDRE) in its promoter (Liu, M. et al. (1996) Genes Dev., 10, 142-153). Clarification of the regulatory mechanisms of p27Kip1 transcription is not only crucial for the understanding of the molecular mechanisms of vitamin D3 action and for the understanding of the early processes during monocyte/macrophage differentiation, but is also extremely important for developing a method for tumor suppression through regulation of p27Kip1 expression. Although the post-transcriptional regulation of P27Kip1 has been studied intensively (Pagano, M. et al. (1995) Science, 269, 682-685; Vlach, J. et al. (1997) EMBO J., 16, 5334-5344; Tomoda, K. et al. (1999) Nature, 398, 160-165), very little is known regarding the transcriptional regulation of the p27Kip1 gene.